Terrestrial communications throughout the world has grown to rely heavily on optical fiber communications technology. And there is an increasing flow of signaling information that requires use of multiple optical fibers in communication links from one point to another. The various origination, termination, and relay points for optical fiber distribution systems form huge matrices—much more complicated than, say, a map of the railroads or the electrical power grid infrastructures in the United States and abroad. In fact, some optical fiber links do run along power lines and railroad right-of-ways. But, they also run under seas, across farmers' fields, down city streets, into campuses and within buildings and homes.
Management of complex fiber optic communication systems requires many different types of specialized optical and electronic equipment to ensure that correct signals are continuously being sent and received with minimum interruptions and that any failures are detected and quickly rectified.
At a very basic level, it is necessary to use an optical tap to extract a portion of the optical signal in each fiber within a transmission cable so that its functionality can be monitored. In some cases, monitoring the total optical power level is sufficient. In other cases where multiple optical channels are simultaneously transmitted on a single fiber using wavelength division multiplexing (WDM), it is often necessary to use arrayed waveguide gratings (AWGs) to separate the individual optical channels before they are directed to monitoring equipment. In other cases, optical splitters and optical switches are also employed for monitoring purposes. Due to the large number of optical fibers used in modern optical communication systems, many optical taps, AWGs, splitters and switches are employed. A multiplicity of these components is typically located inside of an equipment enclosure and these enclosures are mounted in racks that fill equipment bays.
Clearly, it is desirable to reduce both the size and expense of the various pieces of equipment required to accomplish the desired monitoring functions. And this has been an ongoing evolutionary process for all types of equipment used in modern fiber optical communication systems.
The present approach for packaging various optical components like optical taps is to pack some manageable number of them into a container called a cassette that has optical connectors on one or more of its narrow sides. (See for example, “AFL Fiber Inside Plant—Xpress Fiber Management (XFM) Optical Cassettes”—www.AFLglobal.com.) These cassettes are, in turn, closely packed side-by-side into an equipment enclosure that is mounted in an equipment rack such that most or all of the optical connectors on the cassettes face outward for convenient access. (See “Fiber Enclosures: Rack-Mount Enclosure Selection Guide” by Leviton Network Solutions, 2222-222nd Street, S.E., Bothell, Wash. 98021—www.levition.com.) A 19 inch wide equipment enclosure would typically hold ten or twelve side-by-side cassettes.
The LGX equipment design was originally developed by Lucent Technologies (now known as Alcatel-Lucent) but is now broadly used as a defacto standard in the fiber optical communications industry. A number of well know companies including ADC Telecommunications (See “LGX-Compatible (LSX) Preteminated Termination/Splice Panel With Pigtails—User Manual 2009” ADC Telecommunications, Inc, P.O. Box, 1101, Minneapolis, Minn. 55440-1101), Tyco Electronics, and Leviton (See “Fiber Enclosures: Rack-Mount Enclosure Selection Guide” by Leviton Network Solutions, 2222-222nd Street, S.E., Bothell, Wash. 98021—www.leviton.com) are suppliers of the LGX racks, equipment enclosures, and cassettes. Some companies, like Net Optics and MiMetrix Technologies use proprietary equipment enclosure designs for optical taps, but their overall topology is similar to the LGX standard with cassettes that fit into closely spaced openings on the front panel of a rack mounted equipment enclosure. For example, one specific design offered by Net Optics (“Flex Tap Data Sheet” by Net Optics, 5303 Betsy Ross Drive; Santa Clara, Calif. 95054—www.netoptics.com) has a total of 24 side-by-side cassettes each containing two optical taps for a total of 48 taps that are terminated with optical connectors that fits into a standard 19 inch wide rack mounted equipment enclosure that is 1 RU high. (Note: 1 RU corresponds to one unit of rack space that is 1.75 inches high. Typical equipment racks have a total height of 42 RUs or 73.5 inches.) The packaging of optical taps provided by MiMetrix Technologies (“Optical Tap Data Sheet” by MiMetrix Technologies, 11160 C1 South Lake Drive, Suite 190; Reston, Va. 20191—www.mimetrix.com) has a higher density because their design includes twelve optical taps each inside of 8 cassettes whose optical connectors face outward on the front of an equipment enclosure that also has a height of 1 RU. The higher density of optical taps offered by MiMetrix Technologies, 96 taps per 1 RU (8×12=96), is generally considered a more desirable feature than the lower density (48 taps per 1 RU) offered by Net Optics.
Finally, it would be advantageous if the density of various types of optical components like optical taps, AWGs and splitters could be further increased so that less space would be consumed in equipment bays. This is especially relevant for any equipment used in remote monitoring stations because space there is particularly expensive to acquire and maintain.
Also see U.S. Pat. Nos. 5,363,465, 7,218,828, 7,853,112, 7,912,336, 7,939,962, 8,180,192, 8,254,741, and U.S. Patent Application Publication No. 2010/0142907.